Conventional internal combustion engines achieve a relatively fast burn due to the substantially centralized position of the ignition source within the cylinder and the chemical composition of the mixture. The mixture is stoichiometrically correct or nearly so within 2 to 2.5 air/fuel ratios. However, if lean mixtures of the order exceeding 20:1 air/fuel ratio or higher are introduced into the conventional combustion chamber, the mixture may fail to ignite resulting in a total misfire. If initial ignition is achieved, the resulting flame kernel may be quickly quenched also resulting in total misfire. If the flame kernel is not quenched, the combustion proceeds very slowly and the cycle loses its efficiency, or is still burning when the exhaust valve opens. The excessively slow burn may be characterized as a partial misfire.
Lean burn engines that are designed to quickly burn air/fuel mixture ratios of approximately 20:1, but not substantially higher, have been developed and tested for many years. The benefits of lean burn engines include improved fuel consumption, the practically complete elimination of carbon monoxide and low amounts of unburnt hydro-carbons and oxides of nitrogen. These advantages are particularly noticeable under partial loads. However, these engines do not have much of a misfire limit if run at air/fuel ratios higher than 20:1, and at ratios lower than 20:1, produce excess NO.sub.x. The operating limit, then, is very narrow and difficult to control. Switchover to a rich mixture (about 12.5:1) for maximum power output, if abrupt, produces uncontrollable drivability problems. If the switchover is gradual and progressive, on occasion the engine will find itself running at a combination of a high load point and air/fuel ratios around 16.5:1 where knocking is so prevalent as to result in a possible destruction of the engine.
The theoretical advantages of lean burn engines with a single spark-plug have been hindered by misfiring or by ignition that was either too early or too late in the combustion cycle. Previous constructions of lean burn combustion engines that attempted to control misfiring or knocking required complex and expensive approaches of questionable reliability. Alternatively, modified intake port designs have been incorporated which reduce the volumetric efficiency of the engine and thus limit the power output and versatility. Recently, there have been developments which incorporate four valve designs for increased air flow, swirling air motion, and three or more spark plugs positioned about the periphery of the combustion chamber to assure ignition. These engines only operate within the lean regime at some part loads and lower speeds, then switchover to stoichiometric or rich mixtures for higher loads and speeds. The reason that it these engines do not operate in a lean regime at full throttle is that only about 60% of the power potential is realized. Thus, these engines have only a partial lean burn capacity. Further, as earlier explained, the switchover can be very difficult, hard to accomplish, and detrimental to the engine's durability.
What is needed is a combustion engine that incorporates maximum air flow without swirl type air motion which deminishes flow capacity, orderly movement of the air-fuel mixture without decreasing air flow capacity and orderly combustion within the combustion chamber by dual ignition of the fuel/air mixture. These elements in conjunction with the physical and chemical principles of combustion produce positive ignition and fast burn.
The engine with the above fundemental requirements must operate at all conditions of load, speed, and ambient temperature to truly produce an efficient and low emission powerplant. The engine must produce its full output while operating in the lean regime at wide-open throttle (W.O.T.). As previously pointed out, no previous naturally aspirated engine operating lean (at about a 20:1 air/fuel ratio) and at W.O.T. produces more than about 65% of what a comparable engine produces when running with a rich mixture. Thus, to be able to produce the same potential power output, a supplemental air source must be provided. This engine charging can be either by a mechanical supercharger or by a turbocharger. Resultantly, the power potential of such an engine can be comparable to a rich-running counterpart and the engine can maintain good fuel economy, low emissions of HC, CO and NO.sub.x, produce no particulates or visible emissions, and substantially decrease combustion noise. This engine can also start at normal ambient temperatures (75 degrees F.) without enrichment, and with minimal enrichment at colder temperatures. Present homogeneous-charge spark-ignited engines do not have these desirable start characteristics.